Abstract: As a high k material that can be applied to high-density MIM capacitors, Al₂O₃ has a large band gap and good thermal stability, which can effectively reduce the leakage current.Al₂O₃ thin film was prepared by magnetron sputtering, and the leakage current and capacitance of Al₂O₃ thin film were measured under different atmosphere and temperatures, the factors that influence the quality of Al₂O₃ thin film by magnetron sputtering were analyzed and studied. The results show that the leakage current of Al₂O₃ thin films decreases after annealing, and the dielectric properties of samples annealed under oxygen conditions are better than those under nitrogen conditions.After 250 ℃nitrogen annealing, the leakage current of the sample is reduced. The leakage current is about 9 nA at 5 V, and the capacitance fluctuations in the order of 10^-1 pF. The leakage current of samples is only 0.3 nA at 5 V and the capacitance fluctuations is small(~0.03 pF)by oxygen annealing at 250 ℃.